diff --git a/src/ophyd_async/core/_detector.py b/src/ophyd_async/core/_detector.py
index fbc4a7fbec..7212bc7842 100644
--- a/src/ophyd_async/core/_detector.py
+++ b/src/ophyd_async/core/_detector.py
@@ -20,7 +20,7 @@
     WritesStreamAssets,
 )
 from event_model import DataKey
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, NonNegativeInt, computed_field
 
 from ._device import Device
 from ._protocol import AsyncConfigurable, AsyncReadable
@@ -54,7 +54,7 @@ class TriggerInfo(BaseModel):
     #:     - 3 times for initial flat field images
     #:     - 100 times for projections
     #:     - 3 times for final flat field images
-    number: int | list[int]
+    number: NonNegativeInt | list[NonNegativeInt]
     #: Sort of triggers that will be sent
     trigger: DetectorTrigger = Field(default=DetectorTrigger.internal)
     #: What is the minimum deadtime between triggers
@@ -69,6 +69,11 @@ class TriggerInfo(BaseModel):
     #: but publish 2 indices, and describe() will show a shape of (5, h, w)
     multiplier: int = 1
 
+    @computed_field
+    @property
+    def total_frames(self) -> int:
+        return sum(self.number) if isinstance(self.number, list) else self.number
+
 
 class DetectorControl(ABC):
     """
@@ -201,7 +206,7 @@ def __init__(
         self._current_number_index: int = 0
         self._initial_frame: int
         self._last_frame: int
-        self._total_frames: int
+        self._total_frames_to_capture: int
 
         super().__init__(name)
 
@@ -309,18 +314,14 @@ async def prepare(self, value: TriggerInfo) -> None:
             )
         self._trigger_info = value
         self._initial_frame = await self.writer.get_indices_written()
-        self._scan_index: int = 0
         if isinstance(self._trigger_info.number, list):
-            assert all(
-                frame >= 0 and type(frame) is int for frame in self._trigger_info.number
-            ), "Number of frames can only be greater than or equal to 0"
-            self._total_frames = sum(self._trigger_info.number)
+            self._total_frames_to_capture = sum(self._trigger_info.number)
         else:
             assert (
                 self._trigger_info.number >= 0
             ), "Number of frames can only be greater than or equal to 0"
-            self._total_frames = self._trigger_info.number
-        self._last_frame = self._initial_frame + self._total_frames
+            self._total_frames_to_capture = self._trigger_info.number
+        self._last_frame = self._initial_frame + self._total_frames_to_capture
         self._describe, _ = await asyncio.gather(
             self.writer.open(value.multiplier), self.controller.prepare(value)
         )
@@ -331,10 +332,10 @@ async def prepare(self, value: TriggerInfo) -> None:
     @AsyncStatus.wrap
     async def kickoff(self):
         assert self._trigger_info, "Prepare must be called before kickoff!"
-        if self._frames_collected >= self._total_frames:
+        if self._frames_collected >= self._total_frames_to_capture:
             raise Exception(
                 f"Kickoff called more than the configured number of "
-                f"{self._total_frames} iteration(s)!"
+                f"{self._total_frames_to_capture} iteration(s)!"
             )
         if isinstance(self._trigger_info.number, list):
             self._frames_collected += self._trigger_info.number[
@@ -375,7 +376,7 @@ async def complete(self):
             else:
                 if index >= self._trigger_info.number:
                     break
-        if self._frames_collected == self._total_frames:
+        if self._frames_collected == self._total_frames_to_capture:
             self._frames_collected = 0
             await self.controller.wait_for_idle()
 
diff --git a/src/ophyd_async/epics/adaravis/_aravis_controller.py b/src/ophyd_async/epics/adaravis/_aravis_controller.py
index d9761771c6..7bc33b29f9 100644
--- a/src/ophyd_async/epics/adaravis/_aravis_controller.py
+++ b/src/ophyd_async/epics/adaravis/_aravis_controller.py
@@ -30,12 +30,7 @@ def get_deadtime(self, exposure: float | None) -> float:
         return _HIGHEST_POSSIBLE_DEADTIME
 
     async def prepare(self, trigger_info: TriggerInfo):
-        num: int = (
-            sum(trigger_info.number)
-            if isinstance(trigger_info.number, list)
-            else trigger_info.number
-        )
-        if num == 0:
+        if trigger_info.total_frames == 0:
             image_mode = adcore.ImageMode.continuous
         else:
             image_mode = adcore.ImageMode.multiple
@@ -48,7 +43,7 @@ async def prepare(self, trigger_info: TriggerInfo):
 
         await asyncio.gather(
             self._drv.trigger_source.set(trigger_source),
-            self._drv.num_images.set(num),
+            self._drv.num_images.set(trigger_info.total_frames),
             self._drv.image_mode.set(image_mode),
         )
 
diff --git a/src/ophyd_async/epics/adkinetix/_kinetix_controller.py b/src/ophyd_async/epics/adkinetix/_kinetix_controller.py
index b77054c326..8096c4d788 100644
--- a/src/ophyd_async/epics/adkinetix/_kinetix_controller.py
+++ b/src/ophyd_async/epics/adkinetix/_kinetix_controller.py
@@ -27,14 +27,9 @@ def get_deadtime(self, exposure: float | None) -> float:
         return 0.001
 
     async def prepare(self, trigger_info: TriggerInfo):
-        frames: int = (
-            sum(trigger_info.number)
-            if isinstance(trigger_info.number, list)
-            else trigger_info.number
-        )
         await asyncio.gather(
             self._drv.trigger_mode.set(KINETIX_TRIGGER_MODE_MAP[trigger_info.trigger]),
-            self._drv.num_images.set(frames),
+            self._drv.num_images.set(trigger_info.total_frames),
             self._drv.image_mode.set(adcore.ImageMode.multiple),
         )
         if trigger_info.livetime is not None and trigger_info.trigger not in [
diff --git a/src/ophyd_async/epics/adpilatus/_pilatus_controller.py b/src/ophyd_async/epics/adpilatus/_pilatus_controller.py
index f1b2ae31d0..51299cbde9 100644
--- a/src/ophyd_async/epics/adpilatus/_pilatus_controller.py
+++ b/src/ophyd_async/epics/adpilatus/_pilatus_controller.py
@@ -37,14 +37,11 @@ async def prepare(self, trigger_info: TriggerInfo):
             await adcore.set_exposure_time_and_acquire_period_if_supplied(
                 self, self._drv, trigger_info.livetime
             )
-        frames: int = (
-            sum(trigger_info.number)
-            if isinstance(trigger_info.number, list)
-            else trigger_info.number
-        )
         await asyncio.gather(
             self._drv.trigger_mode.set(self._get_trigger_mode(trigger_info.trigger)),
-            self._drv.num_images.set(999_999 if frames == 0 else frames),
+            self._drv.num_images.set(
+                999_999 if trigger_info.total_frames == 0 else trigger_info.total_frames
+            ),
             self._drv.image_mode.set(adcore.ImageMode.multiple),
         )
 
diff --git a/src/ophyd_async/epics/adsimdetector/_sim_controller.py b/src/ophyd_async/epics/adsimdetector/_sim_controller.py
index 9107bffc9b..402d95e68e 100644
--- a/src/ophyd_async/epics/adsimdetector/_sim_controller.py
+++ b/src/ophyd_async/epics/adsimdetector/_sim_controller.py
@@ -31,13 +31,8 @@ async def prepare(self, trigger_info: TriggerInfo):
         self.frame_timeout = (
             DEFAULT_TIMEOUT + await self.driver.acquire_time.get_value()
         )
-        frames: int = (
-            sum(trigger_info.number)
-            if isinstance(trigger_info.number, list)
-            else trigger_info.number
-        )
         await asyncio.gather(
-            self.driver.num_images.set(frames),
+            self.driver.num_images.set(trigger_info.total_frames),
             self.driver.image_mode.set(adcore.ImageMode.multiple),
         )
 
diff --git a/src/ophyd_async/epics/advimba/_vimba_controller.py b/src/ophyd_async/epics/advimba/_vimba_controller.py
index 445306577e..71d41a98f7 100644
--- a/src/ophyd_async/epics/advimba/_vimba_controller.py
+++ b/src/ophyd_async/epics/advimba/_vimba_controller.py
@@ -34,15 +34,10 @@ def get_deadtime(self, exposure: float | None) -> float:
         return 0.001
 
     async def prepare(self, trigger_info: TriggerInfo):
-        frames: int = (
-            sum(trigger_info.number)
-            if isinstance(trigger_info.number, list)
-            else trigger_info.number
-        )
         await asyncio.gather(
             self._drv.trigger_mode.set(TRIGGER_MODE[trigger_info.trigger]),
             self._drv.exposure_mode.set(EXPOSE_OUT_MODE[trigger_info.trigger]),
-            self._drv.num_images.set(frames),
+            self._drv.num_images.set(trigger_info.total_frames),
             self._drv.image_mode.set(adcore.ImageMode.multiple),
         )
         if trigger_info.livetime is not None and trigger_info.trigger not in [
diff --git a/src/ophyd_async/epics/eiger/_eiger_controller.py b/src/ophyd_async/epics/eiger/_eiger_controller.py
index 0ec47017e4..c3c3968adc 100644
--- a/src/ophyd_async/epics/eiger/_eiger_controller.py
+++ b/src/ophyd_async/epics/eiger/_eiger_controller.py
@@ -37,16 +37,11 @@ async def set_energy(self, energy: float, tolerance: float = 0.1):
             await self._drv.photon_energy.set(energy)
 
     async def prepare(self, trigger_info: TriggerInfo):
-        frames: int = (
-            sum(trigger_info.number)
-            if isinstance(trigger_info.number, list)
-            else trigger_info.number
-        )
         coros = [
             self._drv.trigger_mode.set(
                 EIGER_TRIGGER_MODE_MAP[trigger_info.trigger].value
             ),
-            self._drv.num_images.set(frames),
+            self._drv.num_images.set(trigger_info.total_frames),
         ]
         if trigger_info.livetime is not None:
             coros.extend(
diff --git a/tests/core/test_flyer.py b/tests/core/test_flyer.py
index bb48c7dc98..da3e82dce1 100644
--- a/tests/core/test_flyer.py
+++ b/tests/core/test_flyer.py
@@ -141,7 +141,7 @@ async def dummy_arm_2(self=None, trigger=None, num=0, exposure=None):
 
 @pytest.mark.parametrize("number_of_frames", [[1, 1, 1, 1], [2, 3, 100, 3]])
 async def test_hardware_triggered_flyable(
-    RE: RunEngine, detectors: tuple[StandardDetector], number_of_frames
+    RE: RunEngine, detectors: tuple[StandardDetector], number_of_frames: list[int]
 ):
     docs = {}